For incorporation in modules, solar cells on a wafer basis are connected electrically in groups. The cell current must be guided from the cell surface to the cell edge and from there further to an adjacent cell. In most cases, the collection of partial currents from the cell surface and the transfer to the adjacent cell is effected by metallic cell connectors (CC). For contacting the CC, take-off points are provided in the cell surface or at the cell edge.
The conductive cross-section of the CC must be adequate for conducting through currents of several amperes (5-30) per cell with low losses. On the other hand, the CC should only introduce limited mechanical stresses into the contact points. Such mechanical stresses occur between adjacent contact points on individual cells and also on both sides of a bridged cell intermediate space. The mechanical stresses are caused by thermal expansion differences during production and operation of the modules and also deformation of the modules.
In the case of solar cells with contacts on both sides (BSCC), casting the front-side in shadow by the CC must be minimised in addition, this requirement not applying in the case of rear-side contact cells (RSCC).
In the case of BSCC, the cell-side take-off points are disposed on the front-side along straight lines and connected to continuous strips (busbars). On the rear-side a planar metallisation is normal. In the case of RSCC, the take-off points of both polarities are disposed on the rear-side either at the cell edge or in the cell surface. If they are situated at the cell edge, then the CC has no current-collecting function.
In the module production, planar cell connectors (CC) made of coated copper are used. In the case of BSCC, the cross-section thereof is constant and typically is approx. 2 mm×0.15 mm (FIG. 1). They are soldered respectively onto the front side over the entire length on the busbar of a cell and alternate via an offset portion backwards, to the rear-side of the neighbouring cell.
For RSCC with edge contacts, closed, curved or lozenge-shaped CC portions are used for bridging the cell intermediate space, said portions being connected to each other optionally (WO 2005 013 322, WO 2005 122 282).
In DE 43 30 282, U.S. Pat. No. 6,313,395 and JP 62 016 579, a stress-reducing portion in the CC is proposed at the transition between the cells. This embodiment produces high mechanical stress peaks in the CC without significantly lowering the stresses at the take-off points of the cell.
JP 11 312 820 describes a CC with a portion for reducing mechanical stresses in the region of the cells. These portions are configured as raised portions. Their effectiveness is limited because the encapsulation material penetrates underneath during the lamination process and this material subsequently hardens.